This invention relates to styli suitable for use with video disc players of a type in which signals representing changes in electrostatic capacity with respect to a video disc are detected (hereinafter an electrostatic capacity type) and methods of producing such styli, and more particularly it is concerned with a stylus of a shape which difficulty damages the video disc in a reproducing mode and a method of grinding a stylus suitable for obtaining such shape by working on a stylus material.
In video disc players of the electrostatic capacity type, it is essential that the styli do not damage video discs. To this end, it is effective to provide a stylus with a blunt tip at the forward end of its scanning surface in the direction in which it moves in sliding movement while being maintained in contact with a disc. One example of the art of obtaining a blunt tip at the forward end of the scanning surface of a stylus in its sliding direction is disclosed in Japanese Utility Model Laid-Open No. 78501/79 and Japanese Utility Model Laid-Open No. 78502/79 which each show a stylus suitable for use with a video disc having a shape such that a ridge at the forward end portion of the scanning surface of the stylus is continuously rounded and a working method of obtaining such shape. In the shape disclosed in these documents, a portion at which ridges defining the contour of the scanning surface meet each other and a ridge at which one inclined surface meets another inclined surface are rounded, to obtain a continuously rounded ridge. When the ridge is not rounded, the tip of the scanning surface would become sharp. However, when it is rounded, the tip of the scanning surface would become rounded, to thereby enable damage to the video disc to be avoided. The process for rounding the ridge consists in forcing a forward end portion of a stylus or a portion corresponding to the aforesaid ridge at which one inclined surface meets another inclined surface into a sheet-like lap having a diamond compound applied thereto as the latter undergoes elastic deformation. However, some disadvantages are associated with this working process. Difficulties would be encountered in setting working conditions, such as grinding pressure, for obtaining a rounded ridge. Particularly in the vicinity of the point of contact between the forward end portion of the stylus and the sheet-like lap, the grinding pressure might become too high locally to obtain optimum working condition in which the diamond compound is kept in position to properly perform its function without escaping. The result of this would be that a portion near the forward end portion would only be worked on and the forward end portion itself would not be worked on. Thus, the ridge would become sharper after working than before working, thereby causing a large decline in yield.